Contactless power supply technology is widely applicable to a variety of electronic products, such as relatively low power electronic products (e.g., mobile phones, MP3 players, digital cameras, laptops, etc.). Typically, contactless power supply equipment includes a transformer with a transmitting coil (L1) and a receiving coil (L2). Energy can be transmitted from an electric energy transmitter to an electric energy receiver in accordance with magnetic coupling characteristics of the transmitting and receiving coils of the transformer. Such wireless electric energy transmission systems can be operated at a self-inductance resonant frequency. At this resonant frequency, the resistance of the self-inductance and capacitance of the transmitting and receiving coils can be offset. However, when operated at the self-inductance resonant frequency, a less stable current may be generated at the receiving side. This less stable current cannot be supplied to a load, and communication requirements of both the transmitting and receiving sides can be increased for some applications.